Magnetic memories, particularly magnetic random access memories (MRAMs), have drawn increasing interest due to their potential for high read/write speed, excellent endurance, non-volatility and low power consumption during operation. An MRAM can store information utilizing magnetic materials as an information recording medium. Some magnetic memories write to the magnetic material using a current. One such a magnetic memory programs magnetic junctions using spin-orbit interaction (SO) torque.
SO torque-based memories, such as a SO torque magnetic random access memory (SOT-MRAM), utilize conventional magnetic tunneling junctions (MTJs) in conjunction with a line having a high spin-orbit interaction (hereinafter SO line). The conventional MTJ includes a pinned (or reference) layer, a free layer and a tunneling barrier layer between the pinned and free layers. The MTJ typically resides on a substrate and may include seed and capping layer(s) as well as an antiferromagnetic (AFM) layer. The pinned layer and the free layer are magnetic. The magnetization of the pinned layer is fixed, or pinned, in a particular direction. The free layer has a changeable magnetization. The pinned layer and free layer may have their magnetizations oriented perpendicular to the plane of the layers (perpendicular-to-plane) or in the plane of the layers (in-plane). The SO line is adjacent to the free layer of the conventional MTJ. The high spin-orbit interaction may be due to a bulk effect of the material itself (spin Hall effect), due to interfacial interactions (Rashba effect), some other effect and/or some combination thereof.
In conventional SO memories utilizing a free layer having a perpendicular-to-plane magnetic moment, writing is performed by driving a current in-plane (CIP) through the SO line. In order to reliably switch the magnetic moment using the in-plane current, a modest external magnetic field or external magnetic bias is applied. The in-plane current develops an SO torque, which can be used to switch the free layer magnetic moment. Switching to the desired direction is completed using the external magnetic bias. For example, the external magnetic field, an additional AFM layer or biasing structure may magnetically bias the free layer to complete switching to the desired state. In the absence of this external magnetic field, the switching is not sufficiently reliable for use in a magnetic memory.
Although the conventional magnetic junction may be written using spin transfer and used in a spin transfer torque random access memory (STT-RAM), there are drawbacks. In general, for smaller magnetic junction sizes and higher areal density memories, the use of an external field is undesirable. Use of an AFM or biasing structure may result in limited efficiency of the SO torque. Consequently, a mechanism for improving switching in a magnetic memory is still desired.